There is a conventionally used tag search system that performs tagging of data and accumulates the tagged data. With this tag search system, when searching for accumulated data, the data is searched for by specifying a condition using a tag. A Structured document that manages tags and document data in an associated manner is known as a technology for using such a tag search system.
When searching a structured document for a tag, there is a known technology for increasing the processing speed for searching for the tag by compressing the amount of memory or reducing the number of nodes in a tree structure by combining multiple tags into a single tag. Furthermore, there is also a known technology for performing searching while sequentially reading a predetermined amount of text data in a structured document and switching the searching for a tag and a keyword in the tag.
In addition to the structured documents, if a tag is specified on a screen displayed in the Hyper Text Markup Language (HTML) browser, there is also a known tag search system that searches the screen for a tag and displays data corresponding to the searched tag.
Patent Document 1: Japanese Laid-open Patent Publication No. 2002-108850
Patent Document 2: Japanese Laid-open Patent Publication No. 2005-070911
Patent Document 3: Japanese Laid-open Patent Publication No. 2004-038512
However, with the related technology, when searching for large scale tagged data, such as sensor data or a lifelog to which data is sequentially added, random access occurs. Accordingly, there is a problem in that search performance is degraded.
In general, because servers or the like do not retain, in memories, large scale tagged data, the servers retain the data in a disk by using, for example, a database management system (DBMS). If the servers or the like search the large scale tagged data for data that is associated with a specified tag, the servers or the like search for the data by using random access. Accordingly, if a large number of search requests occurs, a large number of random accesses to a disk occurs, and thus it takes a long time to transmit a search result as a response.